The fission yeast Schizosaccharomyces pombe has been utilized as a model system to study mammalian and viral gene regulation. The early adenovirus E2 promoter, which contains two overlapping promoters, has been shown to be efficiently expressed in S. pombe. Transcription from one start site was more efficient than that from the second start site when compared to the start sites utilized in mammalian cells. The TATA motif in the E2 promoter plays a major role in determining the efficiency with which different promoters are expressed in S. pombe. Mutations in the cis- acting element of E2 promoter revealed that the E2F site is recognized in S. pombe. In mammalian cells, E2F plays an important role in the G1 and S phase of the mammalian cell cycle by regulating genes that are essential for the control of the cell cycle. The study of HIV-gag mRNA revealed the inability of the viral Rev protein to enhance the transport of gag mRNA into the cytoplasm in S. pombe. An in situ hybridization method was developed to screen temperature-sensitive (ts) mutants for growth of S. pombe which are unable to transport mRNA to the cytoplasm at nonpermissive temperature. Two ts mutants for mRNA transport, M1 and M2, have been identified which accumulate mRNA in the nucleus at high temperature. Using functional complementation for ts mutant M2, a gene encoding a 40 kd protein was identified and cloned that was able to complement the mRNA transport defect. In addition to this gene having a major role in mRNA transport, it appears to be involved in the regulation of the yeast cell cycle.